This invention relates to a detector, and in particular to a flame detector provided with a sensor, such as a pyroelectric sensor, for detecting the presence of a flame.
A known flame detector includes either a single pyroelectric sensor or multiple pyroelectric sensors, either of which is sensitive to infrared radiation emitted by a flame source. The signal sensed by such a detector is analysed to determine if a flame has been detected. The pyroelectric sensor within the flame detector is sensitive to ambient temperature changes. A flame detector is typically mounted outdoors, and will experience a wide range of ambient temperatures owing, for example, to changing weather conditions. Thus, as the ambient temperature changes, a pyroelectric sensor will produce an output signal which varies with the change in temperature. Certain changes in ambient temperature can produce such a large signal from a pyroelectric sensor that it is the maximum signal it can output. This is undesirable, as detection of a flame cannot then occur. The pyroelectric sensor is more sensitive to temperature changes at low ambient temperatures; whereas, at higher ambient temperatures, greater temperature changes can be tolerated.
An aim of the invention is to provide a flame detector having one or more pyroelectric sensor(s) not susceptible to changes in ambient temperature. In particular, the invention aims to provide a flame detector having a pyroelectric array sensor and a control system for maintaining the temperature variation of the pyroelectric array sensor within predetermined limits, thereby to minimise the level of unwanted signals which result from ambient temperature changes.
It is generally advantageous that, owing to power distribution requirements in installations, the power consumed by a flame detector is kept to a minimum.
Consequently, a further aim of the invention is to provide means for controlling the temperature changes of the pyroelectric sensor, which control means uses minimum power.